1. Field of the Invention
The present invention relates to a frame conversion apparatus and a frame conversion method of converting a video signal comprising a given frame rate into another video signal comprising a frame rate lower than that frame rate.
2. Description of Related Art
In recent years, there is a widespread use of a multi-format camera system using a multi-format video camera for broadcasting or business use that images so-called HDTV (High Definition TeleVision) video signals for input and/or output. Formats for HDTV video signals include the 1080/60i format, the 1080/59.94i, the 1080/50i format, and the like. The 1080/60i format supports images of 1,080 interlace scanning lines and 60 fields per second. The 1080/59.94i format supports images of 1,080 interlace scanning lines and 59.94 fields per second. The 1080/50i format supports images of 1,080 interlace scanning lines and 50 fields per second. Nowadays, there are also developed formats much suited for motion-picture films such as the 24 PsF format having images of 24 frames per second based on progressive scanning and the 23.976 PsF format having images of 23.976 frames per second based on progressive scanning. The 24 PsF format transmits 24P format compliant video signals using the 48i format in terms of transmission.
For convenience of description, the 60i format, the 59.94i format, and the 50i format are generically referred to as a 60i-type format. The 24 PsF format and the 23.976 PsF format are generically referred to as a 24P-type format.
With respect to camera systems, there is developed a multi-format camera system that can image video signals compliant with more than one format for input and/or output instead of imaging video signals compliant with a specific one of these various formats for input and/or output.
FIG. 10 shows an example of such multi-format camera system that comprises a multi-format video camera 200, a Camera Control Unit (hereafter referred to as a CCU) 210, a Master Setup Unit (hereafter referred to as an MSU) 220, and a plurality of multi-format monitors 2301, and 2302. The multi-format video camera 200 can image video signals compliant with more than one format. The CCU 210 controls the multi-format video camera 200 and performs various processes. The MSU 220 controls the CCU 210. The multi-format monitors 2301 and 2302 can reproduce and output video signals compliant with a plurality of formats.
The multi-format video camera 200 is connected to the CCU 210 via an optical fiber cable 140 and images an object under control of the CCU 210. After imaging and obtaining video signals compliant with various formats, the multi-format video camera 200 transmits these signals to the CCU 201 via the optical fiber cable 140. Further, the multi-format video camera 200 can receive a return signal as a video signal compliant a specific format from the CCU 210 via the optical fiber cable 140. In this case, the multi-format video camera 200 presents this video signal to an imaging user or the like via a view finder (not shown) or transmits the video signal to externally connected devices.
The CCU 210 is connected to the multi-format video camera 200 via the optical fiber cable 140. Under control of the MSU 220, the CCU 210 controls the multi-format video camera 200 by supplying it with drive power via the optical fiber cable 140 or transmitting a control signal to the multi-format video camera 200. Also under control of the MSU 220, the CCU 210 processes video signals received from the multi-format video camera 200 via the optical fiber cable 140. Furthermore, under control of the MSU 220, the CCU 210 receives a video signal compliant with one format from the multi-format video camera 200 via the optical fiber cable 140 and converts this signal into a video signal compliant with another format according to output destinations. Under control of the MSU 220, the CCU 210 distributes video signals OP1 and OP2 via a switcher (not shown) and the like and transmits these signals to, e.g., multi-format monitors 2301 and 2302 connected via an HD-SDI (High Definition-Serial Digital Interface) compliant serial bus or the like. When the CCU 210 receives a return signal RET from the outside via the HD-SDI compliant serial bus under control of the MSU 220, for example, the CCU 210 converts the format of this signal into the format for the multi-format video camera 200 and transmits the signal to the multi-format video camera 200 via the optical fiber cable 140.
The MSU 220 is a controller forming the core of the multi-format camera system and controls the CCU 210 connected to the individual multi-format video camera 200 to globally control the multi-format camera system.
The multi-format monitors 2301 and 2302 are provided as an example of devices connected to the CCU 210. The multi-format monitors 2301 and 2302 receive video signals OP1 and OP2 compliant with various formats via the switcher (not shown) and the like and present the received signals to an editor and the like in the multi-format camera system.
When the multi-format video camera 200 images a video signal compliant with one format in this multi-format camera system, the corresponding CCU 210 can process the signal, apply a frame conversion to the signal according to an output destination, and then distribute the signal to devices such as the multi-format monitors 2301 and 2302. The multi-format camera system may be supplied with return signals RET, i.e., video signals compliant with various formats, such as video signals transmitted from another video camera (not shown) or those constituting programs of the other channels. In such case, the CCU 210 can apply a frame conversion and the like to these signals and transmit them to the multi-format video camera 200. The multi-format camera system can handle video signals compliant with not only a specific format, but also a plurality of formats.
Since the above-mentioned multi-format camera system can handle a plurality of formats, the CCU 210 often performs the frame conversion. When the multi-format video camera 200 operates in the 24P-type format, for example, the multi-format camera system can transmit a 24P-type format compliant video signal to the multi-format monitor 2301, wherein this signal can be obtained by not performing frame conversions in the CCU 210. On the other hand, the system can transmit a 60i-type format compliant video signal to the multi-format monitor 2302, wherein this signal can be obtained by applying a frame conversion in the CCU 210 to the 24P-type format compliant video signal. That is to say, the CCU 210 generates a 60i-type format compliant video signal by performing the frame conversion based on the so-called 2-3 pull down technique for the 24P-type format compliant video signal.
More specifically, the CCU 210 performs the frame conversion based on the 2-3 pull down technique as shown in FIG. 11 when converting the 24 PsF format compliant video signal into the 60i format compliant video signal, i.e., when converting a video signal comprising 24 frames per second into a video signal comprising 60 fields per second. As shown in the middle of FIG. 11, the CCU 210 is supplied with the 24 PsF format compliant video signal comprising fields of “A1”, “A2”, “B1”, “B2”, “C1”, “C2”, “D1”, “D2”, and so on. A frame gate signal is supplied from the outside as shown at the top of FIG. 11 and synchronizes with the beginning of field “B1”. Based on the frame gate signal, as shown at the bottom of FIG. 11, the CCU 210 reinserts field “A1” immediately after field “A2”, inserts fields “B2” and “B1” with a reverse order immediately after this field “A1”, inserts fields “C2” and “C1” with a reverse order immediately after field “B1”, and reinserts field “C2” immediately after field “C1”. In this manner, the CCU 210 converts four frames of the input 24 PsF format compliant video signal, i.e., eight fields into ten fields. The CCU 210 can align phases for the succeeding fields by performing the conversion at this cycle and finally generate a 60i format compliant video signal comprising fields “A1”, “A2”, “A1”, “B2”, “B1”, “C2”, “C1”, “C2”, “D1”, “D2”, and so on with an alternate order of odd-numbered and even-numbered fields.
Likewise, the CCU 210 also perform the frame conversion based on the 2-3 pull down technique when converting a 23.976 PsF format compliant video signal into a 59.94i format compliant video signal.
Further, the CCU 210 performs the frame conversion based on the 2-3 pull down technique as shown in FIG. 12 when converting the 24 PsF format compliant video signal into the 50i format compliant video signal, i.e., when converting a video signal comprising 24 frames per second into a video signal comprising 50 fields per second. As shown in the middle of FIG. 12, the CCU 210 is supplied with the 24 PsF format compliant video signal comprising fields of “A1”, “A2”, “B1”, “B2”, “C1”, “C2”, . . . , “K1”, “K2”, “L1”, “L2”, “M1”, “M2”, “N1”, “N2”, “O1”, “O2”, . . . , “W1”, “W2”, “X1”, “X2”, and soon. A frame gate signal is supplied from the outside as shown at the top of FIG. 12 and synchronizes with the beginning of field “B1”. Based on the frame gate signal, as shown at the bottom of FIG. 12, the CCU 210 reinserts field “A1” immediately after field “A2”, inserts fields “B2” and “B1” with a reverse order immediately after this field “A1”, inserts fields “C2” and “C1” with a reverse order immediately after field “B1”, and so on. Immediately after inserting fields “K2” and “K1” with a reverse order, the CCU 210 inserts fields “L2” and “L1” with a reverse order, inserts fields “M2” and “M1” with a reverse order immediately after field “L1”, and reinserts field “M2” immediately after field “M1”. In this manner, the CCU 210 converts 24 frames of the input 24 PsF format compliant video signal, i.e., 48 fields into 50 fields. The CCU 210 can align phases for the succeeding fields by performing the conversion at this cycle and finally generate a 50i format compliant video signal comprising fields “A1”, “A2”, “A1”, “B2”, “B1”, “C2”, “C1”, . . . , “K2”, “K1”, “L2”, “L1”, “M2”, “M1”, “M2”, “N1”, “N2”, “O1”, “O2”, . . . , “W1”, “W2”, “X1”, “X2”, and so on with an alternate order of odd-numbered and even-numbered fields.
In the multi-format camera system, as mentioned above, the CCU 210 can perform the frame conversion based on the 2-3 pull down technique for the 24P-type format compliant video signal to convert the signal into a 60i-type format compliant video signal.
When the multi-format camera system operates the multi-format video camera 200 in the 24P-type format, the CCU 210 maybe supplied with a 60i-type format compliant video signal as a return signal RET. In such case, the CCU 210 performs a reverse frame conversion corresponding to the frame conversion based on the 2-3 pull down technique to generate a 24P-type format compliant video signal.
More specifically, the CCU 210 performs a reverse frame conversion as shown in FIG. 13 when converting a 60i format compliant video signal processed by the same conversion as the frame conversion based on the 2-3 pull down technique as shown in FIG. 11 into a 24 PsF format compliant video signal. As shown at the top in FIG. 13, the CCU 210 is supplied with a 60i format compliant video signal processed by the frame conversion based on the 2-3 pull down technique, wherein the signal comprises fields “A1”, “A2”, “A1”, “B2”, “B1”, “C2”, “C1”, “C2”, “D1”, “D2”, and so on. The CCU 210 then extracts fields “A1”, “A2”, “B1”, “B2”, “C1”, “C2”, “D1”, “D2”, and so on as shown at the bottom in FIG. 13. In this manner, the CCU 210 converts five frames of the input 60i format compliant video signal, i.e., ten fields into eight fields. The CCU 210 can perform the conversion for the succeeding fields at this cycle and finally generate a 24 PsF format compliant video signal comprising fields “A1”, “A2”, “B1”, “B2”, “C1”, “C2”, “D1”, “D2”, and so on by maintaining the correct relation on the time axis with an alternate order of odd-numbered and even-numbered fields.
Further, the CCU 210 performs a reverse frame conversion as shown in FIG. 14 when converting a 50i format compliant video signal processed by the same conversion as the frame conversion based on the 2-3 pull down technique as shown in FIG. 12 into a 24 PsF format compliant video signal. As shown at the top in FIG. 14, the CCU 210 is supplied with a 50i format compliant video signal processed by the frame conversion based on the 2-3 pull down technique, wherein the signal comprises fields “A1”, “A2”, “A1”, “B2”, “B1”, “C2”, “C1”, . . . , “K2”, “K1”, “L2”, “L1”, “M2”, “M1”, “M2”, “N1”, “N2”, “O1”, “O2”, . . . , “W1”, “W2”, “X1”, “X2”, and so on. The CCU 210 then extracts fields “A1”, “A2”, “B1”, “B2”, “C1”, “C2”, . . . , “K1”, “K2”, “L1”, “L2”, “M1”, “M2”, “N1”, “N2”, “O1”, “O2”, . . . , “W1”, “W2”, “X1”, “X2”, and so on as shown at the bottom in FIG. 14. In this manner, the CCU 210 converts 25 frames of the input 50i format compliant video signal, i.e., 50 fields into 48 fields. The CCU 210 can perform the conversion for the succeeding fields at this cycle and finally generate a 24 PsF format compliant video signal comprising fields “A1”, “A2”, “B1”, “B2”, “C1”, “C2”, . . . , “K1”, “K2”, “L1”, “L2”, “M1”, “M2”, “N1”, “N2”, “O1”, “O2”, . . . , “W1”, “W2”, “X1”, “X2”, and so on by maintaining the correct relation on the time axis with an alternate order of odd-numbered and even-numbered fields.
In the multi-format camera system, the CCU 210 can perform the reverse frame conversion for a 60i-type format compliant video signal processed by the frame conversion based on the 2-3 pull down technique to generate a 24P-type format compliant video signal comprising fields maintaining the correct relation on the time axis.
When the multi-format camera system operates the multi-format video camera 200 in the 24P-type format, however, the CCU 210 may be supplied with the return signal RET comprising a 60i format compliant pure video signal not processed by the frame conversion based on the 2-3 pull down technique instead of a 60i format compliant video signal processed by this frame conversion. In this case, if the CCU 210 performs the reverse frame conversion as shown in FIG. 13 or 14, there is generated a 24P-type format compliant video signal comprising fields having the reverse relation on the time axis.
More specifically, the CCU 210 performs a reverse frame conversion as shown in FIG. 15 when converting a 60i format compliant pure video signal not processed by the frame conversion into a 24 PsF format compliant video signal. As shown at the top in FIG. 15, the CCU 210 is supplied with a 60i format compliant pure video signal not processed by the frame conversion based on the 2-3 pull down technique, wherein the signal comprises fields “Ao”, “Ae”, “Bo”, “Be”, “Co”, “Ce”, “Do”, “De”, “Eo”, “Ee”, and so on. The CCU 210 generates a 24 PsF format compliant video signal comprising fields “Ao”, “Ae”, “Co”, “Be”, “Do”, “Ce”, “Eo”, “Ee”, and so on as shown at the bottom in FIG. 15. The 24 PsF format compliant video signal should comprise fields duly arranged in the order of “A”, “B”, “C”, “D”, “E”, and so on. Actually, however, the relation on the time axis is reversed for two fields “Co” and “Be” equivalent to the second frame. In addition, the relation on the time axis is reversed for two fields “Do” and “Ce” equivalent to the third frame.
Furthermore, the CCU 210 performs a reverse frame conversion as shown in FIG. 16 when converting a 50i format compliant pure video signal not processed by the frame conversion into a 24 PsF format compliant video signal. As shown at the top in FIG. 16, the CCU 210 is supplied with a 50i format compliant pure video signal not processed by the frame conversion based on the 2-3 pull down technique, wherein the signal comprises fields “Ao”, “Ae”, “Bo”, “Be”, “Co”, “Ce”, “Do”, and so on. The CCU 210 generates a 24 PsF format compliant video signal comprising fields “Ao”, “Ae”, “Co”, “Be”, “Do”, “Ce”, and so on as shown at the bottom in FIG. 16. The 24 PsF format compliant video signal should comprise fields duly arranged in the order of “A”, “B”, “C”, “D”, and soon. Actually, however, the relation on the time axis is reversed for two fields, “Co” and “Be” equivalent to the second frame. In addition, the relation on the time axis is reversed for two fields “Do” and “Ce” equivalent to the third frame.
The multi-format camera system may allow a mix of two types of video signals, i.e., a 60i-type format compliant video signal processed by the frame conversion based on the 2-3 pull down technique and a 60i-type format compliant pure video signal not processed by the frame conversion as a return signal RET. The CCU 210 performs the same reverse frame conversion for both types of video signals. When the reverse frame conversion is performed for the 60i-type format compliant pure video signal not processed by the frame conversion, there is generated a 24P-type format compliant video signal comprising fields having the reverse relation on the time axis. Accordingly, the multi-format camera system causes exaggerated uncomfortable feeling in an image as the return signal output from the multi-format video camera 200.
This problem is not limited to the conversion from the 60i-type format into 24P-type format. When the pull down function is performed in units of fields, and formats are converted from a high frame rate to a low frame rate, the problem occurs in any of conversions from the i-type format into the i-type format, from the P-type format into the P-type format, from the P-type format into the i-type format, and from the i-type format into the P-type format.